Field of the Invention
The present disclosure relates to a non-aqueous electrolyte storage element.
Description of the Related Art
Along with reductions in sizes and improvements in performances of current mobile devices, properties of non-aqueous electrolyte storage elements having high energy densities have been improved and widely used. Moreover, developments of non-aqueous electrolyte storage elements having the larger capacities and having excellent safety have been conducted, and the above-described non-aqueous electrolyte storage elements have started to be mounted in electric cars.
Under the above-described circumstances, there is a desire for applying a so-called dual intercalation non-aqueous electrolyte storage element for practical use as storage elements having a high energy density and suitable for high-speed charging and discharging. The dual intercalation storage element uses a carbonaceous material in a positive electrode, and therefore elution of elements etc., from the positive electrode does not occur even with high voltage, and the storage element can be operated stably. However, the dual intercalation storage element has a problem that a large amount of gas is generated when a cycle of charging and discharging is repeated. It is assumed that the generation of gas is caused because decomposition of an electrolyte occurs at an interface between an electrode and the electrolyte.
In order to suppress the decomposition of the electrolyte, a solid electrolyte interface (SEI) composed of a decomposition product of the electrolyte, etc., is formed on a surface of a negative electrode in a typical lithium secondary cell. It has been known that the SEI does not have electric conductivity but has lithium ion conductivity, and formation of the SEI suppresses decomposition of the electrolyte.
For example, disclosed is that, by performing a step for performing initial charge on an assembled cell up to a predetermined potential value (preliminary charge treatment), and a step for performing an aging treatment on the cell, to which the initial charge has been performed, by retaining the cell for a predetermined period in a predetermined temperature range, part of an electrolyte component is intentionally reduction-decomposed at the time of the initial charge to cover a surface of the negative electrode with an SEI film composed of the decomposition product of the electrolyte component, and further reduction-decomposition of the electrolyte component on the surface of the negative electrode can be prevented at the time when the cell is normally used (see, for example, Japanese Patent No. 5408509).
Moreover disclosed is that boron per se or a boron-containing functional group is introduced onto a surface of a material by performing a high-frequency heat plasma treatment on a negative electrode composition in a plasma gas atmosphere including BF3, and an SEI can be stably generated on the surface of the negative electrode because of the presence of the boron or the boron-containing functional group (see, for example, Japanese Patent No. 4754109).
Moreover, disclosed is that, by performing a heat treatment on a positive electrode material at 50° C. through 120° C. for 1 hour through 2 months in a discharged state, a passivation film including an SEI and a polymer electrolyte PEI can be formed on a surface of the positive electrode (see, for example, Japanese Patent No. 3121588).